The present invention relates generally to capacitive discharge ignition systems for internal combustion engines, and more specifically to techniques for determining component fault conditions as a function of primary coil voltage in such systems.
Capacitive discharge ignition systems for internal combustion engines are known and commonly implemented in a variety of applications. Such systems typically include an energy storage mechanism, e.g., storage capacitor, coupled to a charging source and to the primary coil of an internal combustion engine ignition coil. An ignition plug is connected across a secondary coil coupled to the primary coil, and discharge of the capacitor through the primary coil induces a high voltage across the secondary coil that ultimately establishes an arc across the spark gap of the ignition plug.
An example of a known capacitive discharge ignition system 10 of the type just described is shown in FIG. 1 and includes a battery 12 or other source of DC potential electrically connected to a DC-DC converter 14. An output of the converter 14 is connected to one end of a capacitor 16 and to one end of a primary coil 18 of an ignition coil 20. The opposite end of the primary coil 18 is connected to a switch 22 that is typically electrically controlled by a control circuit 24 via signal path 26. The opposite ends of the switch 22 and the capacitor 16 are connected to ground potential. A secondary coil 28 coupled to the primary coil 18 is connected across the spark gap of an ignition plug 30 to complete the circuit.
In operation, the DC-DC converter 14 amplifies the voltage supplied by the battery 12 (typically 12 volts DC) to several hundred (e.g., approximately 400) volts to quickly charge the capacitor 16 while the switch 22 is open as shown in FIG. 1. Referring to FIGS. 2 and 3, the control circuit 24 is operable to initiate a spark event by closing switch 22 at time T0. The closing of switch 22 discharges the previously charged capacitor 16 through the primary coil 18, thereby causing the primary coil voltage (PV) 32 to increase sharply (and negatively) from V3 to V4. The electrical pulse provided by capacitor 16 is amplified by the turn ratio of the secondary coil 28 relative to the primary coil 18 (typically on the order of 100:1), thereby causing the secondary coil voltage (SV) 34 to rapidly increase (also negatively) from voltage level V1 (e.g., approximately zero volts). As the secondary voltage SV resultantly increases over time, a voltage level V2 (on the order of 30 kV) will eventually be reached (at time T1) at which the spark gap of ignition plug 30 breaks down (ionizes) and becomes electrically conductive. When this occurs, an electrical arc is established across the spark gap and the secondary coil voltage SV drops sharply to its approximately its pre-discharge voltage (e.g., approximately zero volts). The capacitor 16 continues to discharge until its charge is substantially depleted (at time T2), and the control circuit 24 thereafter opens switch 22 to allow charging of the capacitor 16 via converter 14 for the next spark event.
In modern capacitive discharge ignition systems, each cylinder of the engine typically is provided with a dedicated ignition coil 20 and associated switching circuitry. However, while such complexity allows for excellent control over ignition system operation, it also invites a plethora of potential fault and failure conditions associated with one or more of the various ignition system components. Possible faults typically range in severity from degraded system performance to system and/or engine damage, and it is therefore desirable to provide for fault diagnosis capability. Unfortunately, conventional fault/failure diagnostic techniques for capacitive discharge ignition systems are prohibitively expensive and/or are generally ineffective in their essential purpose.
What is therefore needed is a diagnostic approach for capacitive discharge ignition systems that does not suffer from the drawbacks of known diagnostic systems while also providing for detection of a wide range of component faults, failures and/or degradation.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a method of diagnosing ignition system fault conditions in a capacitive discharge ignition system for an internal combustion engine comprises the steps of measuring a first time difference between an onset of capacitive discharge and occurrence of a reflected spark event in a primary coil voltage of a capacitive discharge ignition system for an internal combustion engine, and determining at least one ignition system fault condition as a function of the first time difference.
In accordance with another aspect of the present invention, an apparatus for determining component fault conditions as a function of primary coil voltage in a capacitive discharge ignition system comprises an ignition coil including a primary coil electrically connected to a capacitor and a secondary coil electrically connected to an ignition plug, means for controllably discharging the capacitor through the primary coil, a spark detection circuit responsive to a primary voltage across the primary coil to compute a first time difference between a beginning of discharge of the capacitor and occurrence of a reflected spark event in the primary voltage, and a processing circuit responsive to the first time difference to determine at least one ignition system fault condition.
One object of the present invention is to provide an apparatus and method for diagnosing fault conditions in a capacitive discharge ignition system based strictly on an analysis of the primary coil voltage.
Another object of the present invention is to provide such an apparatus an method for diagnosing a number of ignition system component fault conditions including, but not limited to, ignition control module (ICM) faults, electrically shorted ignition plugs, worn ignition plugs, electrically shorted ignition coils and external arcing faults.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.